Connection drops over PTP link

Apologies if there have already been posts about this. I'm running a PTP link with cambium 670s and a PMP with the cambium 450i. Have a subscriber using 450b mid-gain model utilizing a VPN also with a soft phone over the same VPN for work. Subscriber is having dropped call issues. Yesterday while running a ping test on the entire network I noticed a few request time outs but only over the PTP link. Subcriber to access point never timed out. Obviously with this occuring it would cause the drop out issues the the subscriber is having but trying to figure out how to resolve this issue and why the time outs would only happen over the PTP link. upgraded subscriber software to in order to add the ultra high priority and priority traffic. Subscriber chose my service specifically to be able to use the VPN software as they had satellite ISP before with too much latency to support the VPN. Drop outs seem to be only between 10-15 seconds and always return but still need to resolve issue. Any suggestions would be appreciated.